1. Field of the Invention
The present invention relates to a pipe for conveying solid matter, particularly for conveying concrete.
2. Description of the Related Art
A pipe of this type disclosed in German Patent 33 24 658 is composed of a cylindrical middle portion and double-layer welding necks at the ends of the middle portion. The cylindrical middle portion may be composed of a single layer. However, the middle portion is preferably constructed with two layers, wherein the core or inner pipe consists of a hardenable carbon steel and the outer pipe consists of a wrought steel. The welding necks also are composed of two layers. The inner layer of each welding neck is of a material which is more resistant to wear than the material of the outer layer.
The inner and the outer layers have the same length and the end faces thereof extend in the same transverse plane. An annular coupling flange of each welding neck may be an integral component of the outer layer. However, the annular coupling flange may also be welded to the outer layer. This known pipe for conveying solid matter has been found useful in conveying solid matter in underground mining and as pipe used in ships, such as, siphons or the like.
If a pipe of the above-described type is used for conveying concrete, it has been found that frequently an increased wear occurs at the inlet side of the pipe even though the inner layer of the welding neck is of a material which is more resistant to wear. A reason for this disproportional wear at the inlet end of a concrete conveying pipe is the play between the two end faces of two abutting concrete conveying pipes and the circumferential pipe coupling which permits this play. The play leads to radial offsetting of two abutting webs with the consequence that the concrete impinges on portions of the end face of the downstream pipe in conveying direction. Another reason is the fact that, in practical use, concrete conveying pipes of one manufacturer are combined with cast bends, conical pipes or Y-pipes of another manufacturer. This means that, even when the differences of the diameters of the pipes which are coupled to each other are initially only slight, an increased wear was observed at the hardened inner layers of the welding necks because of the different resistances to wear of the successive pipes. Thus, depending on the relative positions of the pipes which are coupled to each other in relation to the pipe axis, this results even after a relatively short time in substantial wear of the inlet side of the inner layer of a welding neck almost up to the softer outer layer.
As a result, in the past, a concrete conveying pipe had to be completely replaced even if only the inlet portion was worn over a short length. Accordingly, it was necessary to provide a large number of concrete conveying pipes which are ready for use.
Another requirement of the known pipe for conveying solid matter is that the end faces of the cylindrical middle portion must be precisely worked in order to ensure narrow gaps between middle portion and welding necks after these components have been joined. This is because narrow gaps require sealing rings of small volume. In the past, such sealing rings were absolutely required because, when welding the welding necks to the cylindrical portion, it was necessary to prevent the cooling water necessary for maintaining the hardness of the inner pipe from reaching the welding location during welding and thereby impairing the quality of the welding seam. Therefore, it was necessary in the past to carry out expensive and, thus, uneconomical measures for cutting a piece of pipe required for the middle portions from a length of pipe.
It is, therefore, the primary object of the present invention to provide a pipe for conveying solid matter of the above-described type in which the end portion of the pipe has such a resistance to wear that, independently of the type and the service life of the pipe element arranged upstream of the pipe in conveying direction, i.e., a cast bend, a conical pipe, a Y-pipe, the full service lift of the conveying pipe can be ensured, particularly when concrete is conveyed.